1. Field of the Invention
This invention concerns a fire-resistant, metal subfloor/concrete floor structure incorporating inactive electrical housings, and more particularly method and apparatus for activating an underfloor electrical housing without significantly reducing the fire endurance of the floor structure.
2. Description of the Prior Art
Floor structures particularly adapted for distributing electrical wiring are known which comprise, for example, a metal subfloor including metal cellular units providing enclosed wire carrying cells, a covering layer of concrete, and one or more access housings positioned above the metal cellular units but below the upper surface of the covering layer of concrete. Each housing provides a chamber communicating with at least one of the cells. Each of the access housings may be activated by removing a portion of the covering layer of concrete and installing an activating assembly, thereby to provide ready access to the interior of the chamber and, hence, to the various electrical services at one location in the floor structure. Typical examples of such floor structures and of activating assemblies will be found in U.S. Pat. Nos. 3,303,264 (SAUL et al); 3,609,210 (GURITZ); 3,701,837 (FORK); 3,932,696 (FORK et al).
The use of intumescent material of the type adapted, under fire conditions, to foam and expand has been suggested as a means to fill the interior of the housing with a fire-resistant char, see U.S. Pat. Nos. 3,864,883 (McMARLIN); 3,932,696 (FORK et al). The McMARLIN and FORK et al references neither illustrate nor discuss external fireproofing applied to the lower surface of the metal subfloor.
The use of fireproofing material within insertion-type mountings for electrical outlets which are commonly used in poke-thru systems also is known. See, for example, U.S. Pat. No. 3,803,341 (KLINKMAN) and a publication by ABRAMS et al, Fire Tests of Poke-Thru Assemblies (RD008.D1B) 1971, Portland Cement Association, Skokie, Ill. 60076.